Switch to MELT for testing logging

[gkinsman]

Microsoft.Extensions.Logging.Testing aka MELT on nuget is a useful lib that captures logs and provides access to them in tests. It's also a lot more reliable to test than approvals as approvals rely on the order of output.

Other misc things:

• Fix some issues with property values being types and not strings
• Use FullName everywhere

[codecov]

Codecov Report

Merging #930 (891baac) into main (07afe4e) will increase coverage by 0.41%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #930      +/-   ##
==========================================
+ Coverage   84.19%   84.61%   +0.41%     
==========================================
  Files         120      120              
  Lines        3120     3120              
==========================================
+ Hits         2627     2640      +13     
+ Misses        493      480      -13     

Flag	Coverage Δ
linux	84.48% <100.00%> (+0.28%)	⬆️
macos	53.13% <100.00%> (+0.53%)	⬆️
windows	52.99% <100.00%> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...ools/MessageHandling/Dispatch/MessageDispatcher.cs	93.12% <100.00%> (+5.34%)	⬆️
...ng/AwsTools/MessageHandling/SnsMessagePublisher.cs	96.10% <100.00%> (ø)
...ng/AwsTools/MessageHandling/SqsMessagePublisher.cs	88.67% <100.00%> (ø)
...ng/Middleware/ExactlyOnce/ExactlyOnceMiddleware.cs	92.59% <0.00%> (+14.81%)	⬆️
...aying/Messaging/Monitoring/NullOpMessageMonitor.cs	90.00% <0.00%> (+20.00%)	⬆️

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[slang25]

Very nice

[martincostello]

If this works then just need to rebase #929 once this is merged.